Isohumic

The zonal distribution of soils developed under continental climates was first reported by Dokuchaev, who established in 1883 a map of isohumic curves, between the boreal and sub-arid zones of European Russia.

Even farther north, subarid isohumic brown soils are present from Gourma to Gao (Mali), and in Niger.

The effectiveness of the material varies with the isohumic factor, which is the quantity of humus produced per unit of organic matter (Table 9.1; Kolenbrander 1974).

Although present-day climates of central Europe are favourable to brunification and not to the formation of isohumic soils, in certain favourable sites in central and western Europe some partially brunified isohumic soils occur that are in fact polycyclic soils of biological origin and are entirely Postglacial, being characterised by two successive phases of humification: (i) an older phase of isohumic development; and (ii) a more recent phase of brunification.